Or HaChaim on Genesis 44:33/אור החיים על בראשית מ״ד:ל״ג

1 ישב נא עבדך, "may your servant stay, etc." Although Yehudah had undertaken to bring back Benjamin personally, (43,9) he now relied on the dictum that a messenger appointed by a person can discharge that person's obligation as well as the person who has appointed the messenger (Berachot 34).